Enhancing joint strength using zinc foil and TiO ₂ nanoparticles in dissimilar friction stir spot welding-brazing of AA6061-T6 to EN10130 DC06 steel

The friction stir spot welding-brazing method was applied to create reliable joints between EN10130 DC06 steel and AA6061-T6 aluminum alloy in the presence of zinc interlayer and TiO2 nanoparticles. Zinc interlayer and TiO 2 nanoparticles were incorporated into the joining process to mitigate the formation of detrimental intermetallic phases and improve the joint strength, respectively. The effects of rotational speed and dwell time on joint mechanical properties and microstructure were also investigated. Experimental results demonstrated that optimal friction stir spot joining conditions, achieved at a rotational speed of 900 rpm and a dwell time of 10 s, produced a joint with a fracture force of 2711 N. Nanoparticles significantly improved the joint strength and ductility, resulting in a 43% increase in fracture force (3890 N) and a 105% enhancement in elongation. The increase in strength is attributed to the pinning of grain boundaries by the particles, which prevents their movement and restricts grain growth. The nanoparticles appear to restrict plastic deformation within the zinc foil, leading to a fracture toughness primarily governed by the deformation behavior of the aluminum. The microstructural analysis confirmed the absence of intermetallic phases and insignificant changes to the base materials microstructure. Furthermore, the joint interface exhibited low brittleness and high toughness, which can be attributed to the low heat input during the joining process, resulting in negligible changes in microhardness.